Herrick said the threat was one email message sent to multiple employees at all the locations

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The Department of Agriculture building is shown August 30, 2006 in Washington DC.

The Agriculture Department will reopen some offices Wednesday that were closed after an unspecified email threat.

USDA spokesman Matthew Herrick said offices in Colorado, Maryland, North Carolina and Kearneysville, West Virginia, will open Wednesday with additional security enhancements. USDA offices in Hamden, Connecticut, and Leetown, West Virginia, will remain closed while waiting for security improvements or notifications to union officials.

Herrick said earlier Tuesday that the department had received "several anonymous messages" late Monday that raised concerns about the safety of USDA personnel and facilities. Offices in six locations in five states were closed Tuesday morning "until further notice."

Herrick said the threat was one email message sent to multiple employees at all the locations.

The closed facilities include offices for eight USDA agencies, including the Forest Service and the Food Safety and Inspection Service. Among the sites affected was USDA's sprawling agricultural research center and library in Beltsville, Maryland, where employees were informed of the threat Tuesday morning and sent home. In Fort Collins, Colorado, four buildings at the Natural Resources Research Center — a campus where over 1,000 people work — were closed.

In an email to employees, Agriculture Secretary Tom Vilsack said USDA is closing the offices "due to the serious nature of these threats." He did not characterize the threats, but asked employees to be aware of their surroundings and report any suspicious activity. He said employees could telework or take authorized leave.